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United States Patent |
6,011,246
|
Bonzano
,   et al.
|
January 4, 2000
|
Induction-heating device for surface treating the teeth of a mechanical
part
Abstract
An induction heating device for surface treating the teeth (11) of a
mechanical part on which each tooth (111) has a projecting tip (111s) and
a tooth root linking the tooth to an adjacent tooth, wherein an in duction
coil (12, 12') is spaced from the tooth tips and powered by at least one
high-frequency current source. The coil consists of a set of conductive
segments (24, 24') individually orthogonal to the generatrix (d, d') of
the teeth, located above respective tooth tips and interconnected via
connecting segments (25, 25').
Inventors:
|
Bonzano; Giorgio (Leini, IT);
Criqui; Bernard (Suresnes, FR);
Dias De Sousa; Maria (Paris, FR);
Longeot; Olivier (Talence, FR)
|
Assignee:
|
Renault (Boulogne-Billancourt, FR);
Ensam Bordeaux (Talence, FR);
Saet (Leini, IT)
|
Appl. No.:
|
142170 |
Filed:
|
December 11, 1998 |
PCT Filed:
|
March 14, 1997
|
PCT NO:
|
PCT/FR97/00463
|
371 Date:
|
December 11, 1998
|
102(e) Date:
|
December 11, 1998
|
PCT PUB.NO.:
|
WO97/36459 |
PCT PUB. Date:
|
October 2, 1997 |
Foreign Application Priority Data
Current U.S. Class: |
219/640; 148/573; 219/673; 219/674; 266/129 |
Intern'l Class: |
H05B 006/40; H05B 006/14 |
Field of Search: |
219/640,635,672,673,674
148/573,572,567,569
266/129
|
References Cited
U.S. Patent Documents
3196244 | Jul., 1965 | Wulf | 219/640.
|
4675488 | Jun., 1987 | Mucha et al. | 219/640.
|
4808779 | Feb., 1989 | Cogley | 219/640.
|
Foreign Patent Documents |
2 536 943 | Jun., 1984 | FR.
| |
892 354 | Oct., 1953 | DE | 219/640.
|
966 784 | Oct., 1957 | DE.
| |
94 18808 | Aug., 1994 | WO.
| |
Other References
Evans: "Induction-hardening of Gears", Engineers Digest, vol. 31, No. 12,
Dec. 1970, London GB, pp. 57-68.
|
Primary Examiner: Leung; Philip H.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
Claims
We claim:
1. An induction-heating device for surface treatment of a gear of a
mechanical part on which each tooth has a projecting tip and a gear root
for connection with an adjacent tooth, the generating line of the gear
being non-parallel to the axis of rotation of the mechanical part, the
device comprising an induction coil receiving the mechanical part
concentrically therein with the coil being spaced from the tooth tips,
wherein the coil is supplied by at least one high-frequency current source
for preheating, and the coil comprises an assembly of conductor segments
individually positionable orthogonal to the generating line of the gear
when the mechanical part is concentrically received in the induction coil,
the conductor segments being capable of being respectively located above
the gear tips and being interconnected by connecting segments.
2. A device according to claim 1, characterized by the fact that the
conductor segments extend through an element for concentrating the
magnetic field induced by the said conductor segments.
3. A device according to claim 2, characterized by the fact that the
element for concentrating the magnetic field extends above the median zone
of the gear.
4. A device according to claim 3, characterized by the fact that the
connecting segments extend above a first conductor segment and join
together a second and a third conductor segment situated on both sides of
the first conductor segment.
5. A device according to claim 3, characterized by the fact that the
conductor segments extend beyond the side faces of the gear and are
interconnected by connecting segments distanced from the said gear.
6. A device according to claim 2, characterized by the fact that the
connecting segments extend above a first conductor segment and join
together a second and a third conductor segment situated on both sides of
the first conductor segment.
7. A device according to claim 2, characterized by the fact that the
conductor segments extend beyond the side faces of the gear and are
interconnected by connecting segments distanced from the said gear.
8. A device according to claim 1, characterized by the fact that the
connecting segments extend above a first conductor segment and join
together a second and a third conductor segment situated on both sides of
the first conductor segment.
9. A device according to claim 1, characterized by the fact that the
conductor segments extend beyond the side faces of the gear and are
interconnected by connecting segments distanced from the said gear.
10. A device according to claim 9, characterized by the fact that
short-circuit rings are disposed laterally and on both sides of the gears.
11. The induction heating device of claim 1, wherein the mechanical part is
a steering rack.
12. The induction heating device of claim 1, wherein the mechanical part is
a steering pinion.
Description
The invention relates to an induction-heating device for surface treatment
of the gear of a mechanical part such as a pinion.
Attempts have already been made to subject the gear of a pinion to surface
heating which exactly follows the gear profile, such that it coincides
with the quenched layer.
For this purpose the part to be heated is placed in an induction coil
through which an alternating current is passed.
At high frequency (>100 kHz), however, it has been observed that the
induced currents best follow the tooth profile, but the thermal flux is
convergent at the tip of the gear and divergent at the root thereof.
At medium current frequency (<30 kHz), the induced current density is low
at the tooth tip and high at the tooth root.
In both cases, the hardened quench zone therefore cannot follow the gear
profile, all the more so because the depth of the induced current also
depends on the gear module.
A solution has been sought in two-stage heating comprising successive
heating at low frequency and then at high frequency.
Nonetheless, difficulties are observed in regulating the heating power at
low and high frequency using a single inductor.
More generally, the gear profile must be heated above a transformation
temperature and must then be cooled rapidly by quenching with a liquid to
achieve hardening. The factors which influence the resulting treatment
thickness are depth to which the gear is heated, temperature up to which
the heating temperature exceeds the transformation temperature, and
cooling rate. A circular induction coil situated a short distance from the
undulating gear surface generally produces greater induction heating in
the regions of the gear tips than in the transition regions between the
teeth. The heating temperature and depth are therefore greater in the
outer regions of the teeth. The differently heated zones are therefore
cooled at different rates by the quenching process.
The treatment depth thus obtained and applied to the gear of a pinion is no
longer uniform. The hardening obtained is then excessive in the region of
the tooth tips and insufficient in the region of the connecting surfaces
between the teeth. For successful hardening of the teeth of a toothed
wheel by induction heating, it is therefore necessary to heat the part
uniformly to a previously chosen temperature, directly with
quench-hardening to a controlled depth.
A process for hardening to a uniform depth on the surface of the teeth of
the toothed wheel is described in U.S. Pat. No. 4,675,488. According to
that process, a toothed wheel is disposed in an induction coil having an
axial height or length corresponding to that of the toothed wheel in its
axial direction. The induction coil is supplied briefly with alternating
current at a frequency below 50 kHz, in order to preheat the toothed
wheel. Since the heating depth obtained by induction heating is inversely
proportional to the square root of the current frequency in the induction
coil, preheating penetrates into the toothed wheel. The body of the tooth
is therefore heated to a temperature lower than the temperature for
transformation by quench-hardening of the metal comprising the toothed
wheel. A second preheating stage at lower frequency continues heating of
the body of the toothed wheel and the flanks of the gear.
According to this process, the toothed wheels are first introduced axially
into a medium-frequency induction-heating coil.
The toothed wheel is then displaced axially into a second induction-heating
coil, in which it is subjected to final heating by a greater current at
high frequency.
Each coil must have an axial length longer than the axial length of the
toothed wheel to permit overall heating thereof.
This process, which uses straight annular turns concentric with the pinion,
permits uniform heating of the teeth of straight-gear pinions, since the
induced currents then circulate parallel to the gear edges. When the gear
to be treated is a helical gear with helix angle larger than 20.degree.,
however, circulation of the induced current in the tooth generates
dissymmetric heating of the gear edges. This is due to the fact that the
current is induced orthogonal to the active conductors of the induction
coil and circulates parallel to the axis of rotation of the toothed wheel.
When the generating lines of the gear are no longer parallel, the induced
currents become distributed nonuniformly therein. In this case the
quenching process causes swelling of the tooth flank and a risk of flaking
during engagement of the gear.
The object of the invention is therefore an induction-heating device which
remedies these drawbacks.
In addition, a switching device may be provided to turn on the first and
second current sources in alternation, while the toothed surface can be
displaced in alternating axial movement relative to the coil.
The induction surface of the coil may be directed radially inward or
outward to treat the internal gear of an annular planet gear or the
helical external gear of a pinion.
The invention is advantageously applicable to final induction heating prior
to quench-hardening of the cylindrical toothed surface of a helical-gear
pinion. The invention is also applicable to induction heating of elongated
toothed parts such as steering racks.
The invention relates more particularly to an induction-heating device for
surface treatment of the gear of a mechanical part on which each tooth has
a projecting tip and a gear root for connection with an adjacent tooth, in
which an induction coil is spaced from the toothed surface and is supplied
by at least one high-frequency current source for preheating.
According to the invention, the induction coil comprises an assembly of
conductor segments individually orthogonal to the generating line of the
gear, respectively located above the gear tips and interconnected by
connecting segments.
According to another characteristic of the coil, the conductor segments
extend through an element for concentrating the magnetic field induced by
the said conductor segments.
According to another characteristic of the coil, the element for
concentrating the magnetic field extends above the median zone of the
gear.
According to a particular embodiment of the induction-heating device
according to the invention, the connecting segments extend above a first
conductor segment and join together a second and a third conductor
segment.
According to another particular embodiment of the induction-heating device
according to the invention, the conductor segments extend beyond the side
faces of the gear and are interconnected by connecting segments distanced
from the gear.
According to an additional characteristic of the second particular
embodiment, short-circuit rings are disposed laterally and on both sides
of the gears.
Other characteristics and advantages of the invention will become apparent
on reading a practical example thereof applied to the treatment of a
helical gear of a pinion, with reference to the attached drawing, wherein:
FIG. 1 is a schematic diagram of a device for heating at high and medium
frequencies.
FIG. 2 is a perspective diagram of a helical-gear pinion and of a
structural and positional detail of the induction coil of a first
embodiment of the induction-heating device according to the invention.
FIG. 3 is a developed view of a helical gear and of the induction coil of
the first embodiment.
FIG. 4a is a developed view of a helical gear and of the induction coil
illustrating a second embodiment of the induction-heating device according
to the invention.
FIG. 4b is a developed view of a helical gear and of the induction coil
illustrating a variant of the second embodiment of the induction-heating
device according to the invention.
FIG. 5a is a perspective diagram of the induction coil shown in FIG. 4a.
FIG. 5b is a perspective diagram of the induction coil shown in FIG. 4b.
FIGS. 6 and 7 are characteristic sections VI and VII of the induction coil
shown in FIG. 3.
FIG. 1 represents a toothed pinion 10 whose helical gear 11 is defined by a
generating line (d). An induction coil 12 has a number of turns 13
connected to a low-frequency source in order to produce a magnetic flux
having the value necessary to achieve sufficient heating with a relatively
low current.
Coil 12 has terminals 14, 15, between which there are included 2 turns and
which are connected to the low-frequency source.
Coil 12 has taps 16, 17 connected to a high-frequency source. In the
described example, the high-frequency winding has only one single turn.
The powers to be used will be those suitable for the material comprising
the gear and will depend on the resistivity of the said material.
The lowest frequencies can be on the order of 3 kHz and the highest
frequencies on the order of 400 kHz.
As shown in FIG. 2, which corresponds to a first embodiment of the
induction-heating device according to the invention, the pinion 10 and its
helical gear 11 are disposed concentrically with respect to the coil 12
comprising two turns 13a, 13b. The gear 11 is comprised by elementary
teeth 111, provided with a projecting tip 111s and a root 111p for
connection to an adjacent tooth.
Coil 12 is radially spaced from and disposed at a distance close to the
tooth tips 111s, and is comprised by an assembly of conductor segments 24
which are individually orthogonal to the oblique generating lines (d) of
the respective teeth 111. In this way the segments 24 extend transversely
above the tips 111s.
As shown in FIGS. 2, 6 and 7, two conductor segments 24a, 24b are connected
via their respective extremities to two separate connecting segments 25,
one of the two connecting segments 25 connected to the conductor segments
24a and 24b extending respectively above the conductor segments 24b and
24a. This arrangement permits the conductor segments 24 to be connected
electrically without allowing a large induced current to be created in
gear 11 due to passage of current through connecting segment 25. In
effect, these connecting segments 25 on the one hand are distanced from
the gear tip 111s, thus greatly reducing the intensity of the currents
induced by them in gear 11, and on the other hand they pass above a
conductor segment 24, which thus acts as pumping short circuit for the
currents induced by connecting segments 25. The current circulating in
gear 11 is then mainly the current induced by the conductor segments 24,
which are orthogonal to the generating line of gear 11, thus allowing
homogeneous heating of the gear edge to be achieved.
As shown in FIG. 3, the conductor segments 24 can extend through an element
34 for concentrating the induced magnetic field in such a way as to
reinforce the heating of the median zone of gear 11. Such an element is
comprised by materials 34 of high magnetic permeability which reinforce
the currents induced by segments 24.
The first embodiment of the induction-heating device described hereinabove
is advantageously applied to large-dimension gear mechanisms in which the
width of gear 1 is small relative to the diameter D (D/I>4) and in which
the helix angle of the gear is moderate (from 20.degree. to 40.degree.).
FIGS. 4a and 5a correspond to a second embodiment of the induction-heating
device according to the invention, characterized by high load impedance.
FIGS. 4b and 5b correspond to a variant of the second embodiment,
characterized by low load impedance. FIGS. 4a and 4b represent a developed
view of pinion 10 and of its gear 11 surrounded by the induction coil 12'.
Induction coil 12' is comprised by conductor segments 24' orthogonal to
the generating line d' of the gear and interconnected by connecting
segments 25'. These connecting segments 25' are distanced from the edges
of gear 11 and disposed parallel to the edges of pinion 10. This
arrangement permits the intensity of the currents induced in gear 11 by
the current circulating in connecting segments 25' to be reduced
considerably by increasing the distance between the connecting segments
25' and the edges of gear 11. The influence of these connecting segments
25' on the currents induced in the gear can be further reduced by adding
short-circuit rings 27 disposed laterally at the gear side faces, thus
permitting a reduction of the heating and therefore of the thickness of
quenching at the teeth side face. This reduction of heating of the teeth
side face can be desirable in the case of non-chamfered gears.
As shown in FIGS. 4a to 5b, the conductor segments 24' can extend through
an element 34', comprised by materials of high magnetic permeability, for
concentrating the induced magnetic field. In this case, the element 34'
concentrates the magnetic field and the current induced in the median zone
of the teeth, and prevents any overheating of the lateral edge of the
gear.
This second embodiment of the induction-heating device is advantageously
applicable to gear mechanisms of small dimension and gear with large width
relative to the diameter D (D/I<5) and for large helix angles of the gear
(>30.degree.).
The induction-heating device according to the invention therefore permits
an improvement in the symmetry of heating of the edges of gears of a
pinion, and it can be advantageously applied to induction coils which are
supplied successively by currents at two frequencies and which, because of
their large heating powers, exacerbate the differences in circulation of
induced currents, and application thereof permits the fatigue strength of
gears to be substantially improved.
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